"The game, as far as I'm concerned, boils down to the fourth inning," Rockies manager Jim Tracy said. "Jonathan made some great pitches, then he had a momentary lapse and made a bad pitch to Ian Kennedy. Next thing you know they have four runs on the board, and really it's the difference in the game."
The loss marked the Rockies' seventh in their last nine games.
Sanchez left after tossing four innings and surrendering five runs on six hits. The left-hander has allowed five or more runs in six of his 13 starts this season.
"I felt pretty good, I thought I made some good pitches," Sanchez said. "I was over the plate more than I'm used to. It was one of those days where you make a mistake and you have to pay for it."
Sanchez, who spent the first six years of his career in San Francisco, was 1-6 with an 8.06 ERA this season with the Royals before the trade. From 2009-11 in the NL, however, Sanchez was 25-28 with a 3.75 ERA, and his .204 opponents' average in 2009 led the Majors.
"I didn't know what to expect, because I hadn't seen him in a while," Tracy said. "He's had some trouble spots over his course of time in Kansas City, but we saw some good breaking pitches from him and his fastball at times was well located. Like I said, though, he had the one mishap to Kennedy."
The aforementioned blunder by Sanchez came in the fourth after Colorado received a gift from Miguel Montero, who hit a ball off the right-field wall but was tagged out heading to second base with runners already occupying second and third.
After Chris Young popped out, Sanchez intentionally walked Ryan Roberts to load the bases with two outs -- setting up Kennedy to deliver the biggest blow of the night and give the D-backs a 4-0 lead.
"I got Kennedy in a good count and then I made a mistake over the plate," Sanchez said. "It was supposed to be a fastball away and it ran through the middle."
The abrupt change in momentum left Tracy wondering what if after the game.
"You get the guy out and it's a zero on the scoreboard," Tracy said. "You might be out there to win the game in relation to what else took place, because we shut them down after the fourth inning."
On the other side of the coin, Kennedy was just as surprised he hit the ball as hard and as far as he did.
"That's happened a couple of times, where they've walked the guy in front of me to load the bases and I haven't hit the ball very good at all this year," he said. "I just saw the ball and tried to make solid contact. It felt good to actually do something in that situation."
Offensively, things weren't much better for the Rockies. Batting third, Carlos Gonzalez hit his 20th home run of the season in the ninth inning to snap a 0-for-28 drought over the last two games from the middle of the order.
"Quite frankly, offensively we haven't done much at all, very little in fact," Tracy said. "That makes it pretty tough to generate any additional offense."
D-backs first baseman Paul Goldschmidt opened the scoring with a solo homer in the second. Josh Rutledge got the Rockies on the board in the fifth with his first big league homer to cut the Arizona lead to 5-1.
After Sanchez left the game, Carlos Torres pitched three hitless frames to keep the Rockies within striking distance, even though the offense remained mostly punchless.
"Probably the best outing Torres has had in between the couple times he's been back and forth with us in the big leagues," Tracy said. "He threw a lot of strikes, a lot of quality strikes. He kept the game where it was at, we just weren't able to do anything."